Support configuration env variable replacement

We want to support environment variable replacement in the configuration
similarly to how it is done in llama-stack.

Example use case / motivation:

The config, which since 3f7ed75 can
contain a password to a database, requires users to move their entire
config to a Kubernetes secret, as it now contains sensitive information,
rather than a configmap. If instead we supported environment variable
replacement, users could keep their config in a configmap and just set
the password in a secret as k8s allows you to load secret values as
environment variables in pods.

Since users of lightspeed-stack are already familiar with the syntax
for environment variable replacement from llama-stack, we can use the
same function from llama-stack to handle this.

Author: omertuc

src/configuration.py

@@ -3,6 +3,10 @@
 import logging
 from typing import Any, Optional
 
+# We want to support environment variable replacement in the configuration
+# similarly to how it is done in llama-stack, so we use their function directly
+from llama_stack.core.stack import replace_env_vars
+
 import yaml
 from models.config import (
     Configuration,
@@ -16,6 +20,7 @@
     DatabaseConfiguration,
 )
 
+
 logger = logging.getLogger(__name__)
 
 
@@ -38,6 +43,7 @@ def load_configuration(self, filename: str) -> None:
         """Load configuration from YAML file."""
         with open(filename, encoding="utf-8") as fin:
             config_dict = yaml.safe_load(fin)
+            config_dict = replace_env_vars(config_dict)
             logger.info("Loaded configuration: %s", config_dict)
             self.init_from_dict(config_dict)